The free-fluid phase of plaque (plaque fluid) and a low pH elution were assayed for IgA, IgG, IgM, complement, transferrin, alpha 2 macroglobulin, albumin, lysozyme, amylase and total protein. The proteins were present at levels suggesting the contribution of both saliva and gingival exudate. Immunoglobulin A, lysozyme and complement were found bound to the solid phase suggesting their participation in host defense.